Pope Benedict XVI delivers his "Urbi et Orbi" (to the City and to the World) speech from the central loggia of St. Peter's Basilica, at the Vatican, Tuesday, Dec. 25, 2012.

(CBS NEWS) -- Vatican officials said Monday that Pope Benedict XVI had announced to
his senior clergy that he would resign his position as the head of the
Roman Catholic Church on February 28, according to multiple news
agencies which received a transcript of his remarks.

Benedict has dealt with health issues for some time, and the
85-year-old announced his decision in Latin during a meeting of Vatican
cardinals Monday morning, according to the Associated Press. The move
took almost all Vatican observers, and millions of Catholics around the
world, by surprise.

He said that because of his advanced
age and diminishing strength, he didn't feel he could carry on the job.
Reuters quoted the Pope as saying he was "fully aware of the gravity" of
his resignation.

The pope's brother, Georg Ratzinger,
told a news agency in Germany that the pontiff had been advised by his
doctor not to take any more transatlantic trips and had been considering
stepping down for months.

Talking from his home in
Regensburg to the news agency dpa, Georg Ratzinger said his brother was
having increasing difficulty walking and that his resignation was part
of a "natural process."

"His age is weighing on him," the 89-year-old said of his 85-year-old brother. "At this age my brother wants more rest."

The 265th Pontiff, Benedict will be the first leader of
the Church to step down voluntarily in almost six centuries. He has led
the Church since 2005 through a tumultuous time that has seen him
criticized for his handling of the scandal related to years of sexual
abuse of young parishioners by priests and other clergy, and senior
church officials' alleged moves to hide those actions.

Benedict has also had to deal with the fallout of a traitor in his own ranks -- his butler was convicted in 2012 (video) of stealing personal documents from Benedict's living quarters and leaking them to the media.

Benedict's
decision sets the stage for a conclave to elect a new pope before
the end of March. Vatican communications advisor Greg Burke told "CBS
This Morning" that the pontiff's sudden departure doesn't leave a lot of
time for Church officials to pick a replacement if they want the post
filled before Easter, but he also noted that there won't be the usual
delay of nine days mourning for a pope who dies in office.

"We certainly hope to have a new pope by Easter," said Burke.

Burke said he only found out about the pope's decision a couple hours before Benedict announced it to the cardinals.

"It
was a surprise, but maybe not a shock," said Burke, who had worried
about the aging pontiff's health increasingly in recent weeks. "I was
always very nervous when I saw him going up and down steps," added
Burke, noting that Benedict had problems with at least one of his knees.
He said the pontiff did not, however, have any immediate, grave medical
condition that he was aware of.

The following is a
transcription of part of the remarks Pope Benedict made in Latin to his
cardinals on Monday morning, which was released to the media by the
Vatican (Click here to read the full text):

"I
have come to the certainty that my strengths, due to an advanced age,
are no longer suited to an adequate exercise of the Petrine ministry.

I am well aware that this ministry, due to its essential spiritual
nature, must be carried out not only with words and deeds, but no less
with prayer and suffering.

However, in today's world, subject to so many rapid changes and shaken
by questions of deep relevance for the life of faith, in order to govern
the bark of Saint Peter and proclaim the Gospel, both strength of mind
and body are necessary, strength which in the last few months, has
deteriorated in me to the extent that I have had to recognize my
incapacity to adequately fulfill the ministry entrusted to me."